The invention relates to a fluid-actuated impact hammer for advancing objects in the ground, and particularly to an impact hammer by which a drill piping can be advanced into the ground.
From Canadian Patent 1 038 725 and U.S. Pat. No. 4,006,665, hydraulic impact hammers are known which comprise a working piston movable in a working cylinder. The working piston performs a working stroke at the end of which it strikes upon an anvil connected to the drill rods, and thereafter, it performs a return stroke. The working strokes and return strokes of the working piston are controlled by a control piston which, in turn, is controlled depending on the respective position of the working piston. Such impact hammers are suited for an effective advance of objects into the ground.
Difficulties do often arise when objects, as, e.g., drill pipes, are to be withdrawn from the ground. At the lower end of a drill pipe, there is a conical drill bit. Upon withdrawal of the drill piping, this drill bit gets stuck at the drill hole with a dowel effect. Commonly, the impact hammer is then actuated upon withdrawal to vibrate the drill rods and release the pipe.
From U.S. Pat. No. 5,259,464, an impact hammer for drill rods is known wherein the impact direction of the impact piston is reversible by reversing the impact hammer on the drill piping. This solution prerequires that the housing of the impact hammer is open at both ends. Considerable mounting efforts are required to reverse the impact hammer, and it can hardly be performed on the drilling site.